The present disclosure relates generally to radio communications systems and methods. In conventional trunked radio systems, such as Terrestrial Trunked Radio (TETRA), Project 25 (P25) or the like, multiple subscriber units (SU) can participate in various voice and/or data sessions therebetween via various available channels (CH1 . . . CHn). These systems utilize a dedicated control channel (CC) for coordination of various activity in the system and transmission and exchange of control information, such as, for example, voice call requests and/or grants, mobility requests and/or grants, data context activation requests, etc. As system activity increases and the number of SUs scale, the single dedicated control channel may become a limitation. For example, in an exemplary trunked radio system, the control channel can be a single inbound frequency for multiple access control using a slotted ALOHA algorithm. For a single try, the channel efficiency is about 36.8%. For multi-try (up to 5 tries according to an exemplary design), the inbound CC can support around 7 Inbound Signaling Packet (ISP)/sec with ˜95% reliability. As the SU requests increase, such as push-to-talk (PTT) requests for voice, mobility, and/or data context activation requests, the increased collisions on the inbound (IB) CC may cause the reliability of ISP transmission to drop and may make the channel unusable. As a result, it could take longer time (up to five tries with back off timers) to send in a successful request. In case of a voice call request, the access time to a working voice channel would be delayed and could potentially cause audio truncation at the beginning of a voice transmission.
Conventional techniques to address control channel limitations include assigning additional control channels to increase capacity. However, such techniques reduce available working channels (i.e., reducing available resources available for voice and/or data traffic channels) and still encounter the same aforementioned limitations, namely control channel resources are fixed.
Accordingly, there is a need for a method and apparatus to increase service capacity in radio communication systems using idle working channels as flexible control channels.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.